The invention provides a timing circuit using a counter which is incremented by an oscillator to yield a delayed output at a given count. The counter is enabled by an input on signal and clocked by the oscillator to the given count, and then outputs an output ON signal delayed from the input ON signal by the given count. The counter is disabled by an input OFF signal and outputs an output OFF signal without delay. A second counter is responsive to the first counter for outputting the delayed output ON signal without further delay, and for delaying the output OFF signal.
A first adjustable frequency oscillator clocks the first counter and controls the ON delay. A second adjustable frequency oscillator clocks the second counter and controls the OFF delay. Both the input ON and input OFF signals are input to the first counter. Each counter includes gate means connected between the output and input of the counter for inhibiting and for allowing clocking therethrough of the respective counter from the respective oscillator.
The circuit is characterized by expanded timing range, reduced power consumption and improved adjustment resolution. Though not limited thereto, the circuit was developed for proximity switches and is particularly useful in photoelectric type proximity switches for providing a delayed output signal following a given sensed condition. The wide range together with the low power consumption makes the circuit ideal for such proximity switch applications.